This invention relates to an electrical bridge for providing a low resistance junction between confronting electrical contact surfaces, and more particularly a bridge for use with electrical conductor cables and other circuit elements to be electrically joined with one another, which maintains low resistance contact integrity over time, by protecting the contacting surfaces from vibration and corrosion caused by exposure to the elements.
Electrical junctions in the prior art generally rely on direct pressure contact between confronting, electrically conductive contacting surfaces. The contact surfaces are of generally complimentary shape and are presumed to be in close enough contact over sufficient area portions thereof to minimize electrical resistance across the junction, thereby providing an electrically efficient connection. However, various practical factors may reduce the efficiency of such unions. For example, any high spots present on either surface can have an adverse effect on contact efficiency by preventing the contacting surfaces from being sufficiently joined over a remainder thereof. Sheering movement between the contact surfaces brought about by vibration and the like, may also adversely affect electrical integrity of the connection during prolonged use in environments where such factors are present, such as, for example, in automobile applications. Moreover, pitting of the surfaces caused by exposure to the elements, or electrical arching due to imperfect electrical contact, can result in deterioration of the connection over time. In addition, because the contacts are brought together in close, but not perfect contact, capillary action may exacerbate the deleterious effects of exposure to moisture by drawing any liquid present at the periphery of the contact surfaces inwardly to the inner contact regions.
A particularly challenging application for low-resistance connectors relates to the connection of electrical cables to storage batteries of automobiles. Because of high current demand, particularly during start-up, a low resistance battery/cable connection is essential for proper automobile operation. Progressive deterioration of an initially satisfactory electrical connection is common in prior art battery connectors, due to the harsh environmental factors to which components within the engine compartment are typically exposed. Such contact degradation will adversely affect start-up, and a resultant failure to provide proper charging voltage may potentially reduce battery life.
Storage batteries of the type used in automobiles, trucks and other like vehicles generally include terminal posts comprised of lead alloy material, and are either cylindrical in shape when side mounted, or frustro-conically shaped when located atop the battery. When adapted for use with a side terminal battery, a conventional cable connector typically includes a thick, washer-shaped portion, which overlays the flat end of the cylindrical battery terminal, and is fastened thereto by a bolt received in a threaded central hole in the terminal post. In the case of top terminal batteries, the connector consists of a generally U-shaped structure including a pair of parallel arms projecting from the open end of the U, through which extends a bolt threaded into a companion nut, allowing the connector to be tightened about the post received through the U-shaped portion. Such connectors as described above have generally been either die cast from various alloys of lead, copper or zinc, or alternatively stamped and formed from sheet metal.
Secure mechanical connection is essential, particularly in automotive applications, since electrical resistance must be optimally reduced to meet high current demand. It had heretofore been assumed that the relatively large available surface area of contact between the cable connector and the battery terminal would alone be sufficient to consistently provide a conductively efficient union when contact surfaces were brought into pressurized alignment. However, empirical evidence has proved otherwise. Even when initially attained, a mechanically secure, low resistance connection achieved as described above, may be compromised by sustained vibration. Exposure to air, water, engine oil vapors, spilled anti-freeze, etc., as well as extreme temperature variations, have been invariably shown to further reduce electrical efficiency of the connection through corrosion.
Because of the commercial desirability of developing a low resistance car battery/cable connector, attempts have been made in the prior art to improve performance of such devices by improving electrical continuity between cable and battery, and further providing enhanced resistance to angular rotation. For example, U.S. Pat. No. 5,087,214 issued to Dewar, describes one such attempt in which the inner surface of a connector is provided with inwardly facing edges adapted to penetrate the relatively soft material of the terminal post and inhibit rotation of the connector about the post. Although effective in providing improved conductivity and resistance to vibrational disturbance, the invention does not have application for side terminal batteries, nor does it address the problem of corrosion due to exposure to the elements for either top or side terminal batteries. Moreover, the connector described in the above patent cannot be easily adapted to an existing conventional battery connection, its use requiring removal and replacement of an existing conventional cable connector.
Another particularly problematic electrical connector application involves electrical power distribution. These systems generally rely on electrical transmission via buss bars which are bolted in overlapping engagement to one another, to produce a pressure contact electrical union between confronting surfaces. Because of the high current load of such applications, an increase of resistance of such union may result in generation of significant heat, sometimes extreme enough to melt the buss bars, potentially causing catastrophic failure of the connection. Exposure to water and other environmental factors may reduce the long-term effectiveness of such buss bar connections, as generally noted above, adding to the potential of system failure. Therefore it would be highly desirable to provide an improved low resistance connection between confronting contact surfaces suitable for use in high-power applications that reliably maintains contact integrity over time.